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    LK-99: the room-temperature superconductor that wasn't

    Also known as LK99, copper-doped lead apatite, Pb10-xCux(PO4)6O

    LK-99 is a copper-doped lead apatite that a July 2023 preprint claimed was a superconductor at 400 K (127 °C) and ambient pressure.[1] Within weeks, replication showed that pure LK-99 is an insulator and that a copper sulfide impurity explained its superconductor-like behaviour, making it a case study in fast, open verification.[2][3][4]

    Editor reviewedUpdated Materials sciencePhysicsScience
    Key facts

    The claim

    On 22 July 2023 a preprint titled “The First Room-Temperature Ambient-Pressure Superconductor” claimed that a copper-doped lead apatite called LK-99 superconducts at 400 K (127 °C) or above, with no applied pressure.[1] The authors attributed the effect to a slight structural distortion caused by copper replacing some of the lead.[1]

    The stakes were high. The best confirmed ambient-pressure superconductors are still about 140 °C short of room temperature, and a material that closed the gap would remove the need for expensive cooling.[5][6] Independent groups quickly tried to reproduce it.[4]

    How it unravelled

    A real superconductor shows two signatures: zero electrical resistance and expulsion of magnetic fields.[7] Replication efforts tested both.

    • The resistance drop. An August 2023 study showed that LK-99 samples contain copper sulfide (Cu2S), which goes through a structural phase transition near 385 K. That transition causes a sharp fall in resistivity, which looked like a superconducting transition. The samples never reached zero resistance.[3]
    • The pure material. A team that grew phase-pure, transparent single crystals of the compound found them “highly insulating” and ruled out superconductivity.[2]

    Together these explained the headline observations. The resistance drop came from the impurity, and pure crystals showed only the diamagnetic response of an ordinary non-magnetic insulator.[3][2]

    By 16 August 2023, Nature’s news team reported that replication efforts had established that LK-99 is not a superconductor and had explained its superconductor-like behaviour.[4]

    Why it matters as a case study

    LK-99 played out on a preprint server rather than in a peer-reviewed journal. That made it unusually fast: the claim was posted and tested by independent groups within weeks.[1][4] The episode came in the same year as a separate room-temperature claim, for a nitrogen-doped lutetium hydride under pressure, which Nature retracted in November 2023 after most of its authors requested it and most other groups failed to reproduce the result.[8]

    For readers, two practical lessons follow from the evidence. A resistance drop is not enough on its own, because impurity phase transitions can mimic one.[3] And phase-pure samples, made independently, are the decisive test.[2] The room-temperature superconductivity debate discusses how the field now weighs such claims, and how superconductivity works explains the physics.

    What the evidence showed

    The original preprint said superconductivity was proved by five signatures: the critical temperature, zero resistivity, critical current, critical magnetic field and the Meissner effect.[9] The replications tested the key ones. The copper sulfide study saw a sharp, superconductor-like transition, but with thermal hysteresis in both resistivity and magnetic susceptibility. That pattern fits a structural phase change, not a superconducting transition.[10] The phase-pure crystal study found copper spread unevenly through the sample. The crystals showed the diamagnetic response of an ordinary non-magnetic insulator plus a small ferromagnetic component, and no sign of any phase transition.[11]

    The record that LK-99 claimed to smash still stands far from room temperature. The current ambient-pressure record of 151 K, reported in March 2026, came from a cuprate after a pressure-quench treatment.[12]

    Questions readers ask

    Is LK-99 a superconductor?

    No. Phase-pure single crystals were found to be highly insulating, and the researchers ruled out superconductivity.[2]

    Why did LK-99 look like a superconductor?

    A copper sulfide impurity undergoes a structural phase transition near 385 K that causes a sharp drop in resistivity, mimicking a superconducting transition, without zero resistance.[3]

    How long did it take to debunk LK-99?

    About three and a half weeks. The preprint appeared on 22 July 2023, and by 16 August Nature reported that replication efforts had solved the puzzle.[1][4]

    Sources

    Each numbered claim is a statement we checked against the sources listed with it. Status shows how well established it is.

    1. [1]

      On 22 July 2023 a preprint claimed that LK-99, a copper-doped lead apatite, was a superconductor at 400 K (127 °C) or above at ambient pressure, attributing this to a slight structural distortion from copper substituting for lead. confirmedas of 2026-10-10

    2. [2]

      In August 2023 researchers who grew phase-pure single crystals of the LK-99 compound found them highly insulating and transparent and ruled out superconductivity. confirmedas of 2026-10-10

    3. [3]

      An August 2023 study attributed LK-99's sudden resistivity drop to a structural phase transition of a copper sulfide (Cu2S) impurity near 385 K, and observed no zero resistance. confirmedas of 2026-10-10

    4. [4]

      By 16 August 2023 Nature's news team reported that replication efforts had established LK-99 is not a superconductor and explained its superconductor-like behaviour. confirmedas of 2026-10-10

    5. [5]

      Even after the 151 K record, roughly 140 degrees Celsius still separate the best ambient-pressure superconductors from room temperature (about 300 K). confirmedas of 2026-10-10

    6. [6]

      Most superconductors must be cooled to extremely low temperatures, which makes them expensive and difficult to use; the University of Houston team says room-temperature superconductivity could dramatically improve power grids, medical technologies and energy systems. confirmedas of 2026-10-10

    7. [7]

      Superconductivity is the property of certain materials to carry direct current with no energy loss when cooled below a critical temperature; superconductors also expel magnetic fields as they enter the superconducting state. confirmedas of 2026-10-10

    8. [8]

      On 7 November 2023 Nature retracted a March 2023 paper claiming room-temperature superconductivity in a nitrogen-doped lutetium hydride, after eight of its 11 authors requested retraction; most other groups had failed to reproduce the result. confirmedas of 2026-10-10

    9. [9]

      The original LK-99 preprint said its superconductivity was proved by the critical temperature, zero resistivity, critical current, critical magnetic field and the Meissner effect. confirmedas of 2023-07-22

    10. [10]

      The Cu2S study observed a sharp superconducting-like transition with thermal hysteresis in both resistivity and magnetic susceptibility, consistent with a structural transition rather than superconductivity. confirmedas of 2023-08-08

    11. [11]

      The phase-pure LK-99 crystals showed an uneven distribution of copper, the diamagnetic response of a non-magnetic insulator with a small ferromagnetic component, and no anomalies indicating phase transitions. confirmedas of 2023-08-11

    12. [12]

      In March 2026 a University of Houston team reported a superconducting transition temperature of 151 K at ambient pressure in the mercury cuprate Hg-1223, beating the 133 K ambient-pressure record that had stood since 1993. reportedas of 2026-10-10

    13. [13]

      In April 2026 a SUSTech-led team reported (La,Pr)3Ni2O7 films with a superconducting onset of 63 K and zero resistance at 37 K at ambient pressure, published in National Science Review. reportedas of 2026-10-10

    Revision history (2)
    1. Page created.
    2. Added what the original preprint claimed as proof and further detail from the replication studies.

    Created Oct 10, 2026. Last reviewed by an editor on Oct 10, 2026. Next scheduled review: Jan 10, 2027.

    Cite this page

    "LK-99: the room-temperature superconductor that wasn't." ContentLora, updated Oct 10, 2026. https://contentlora.com/wiki/lk-99

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